CN109790501B

CN109790501B - Device for exposing an algae solution to light, associated photobioreactor and method of implementation

Info

Publication number: CN109790501B
Application number: CN201780059255.7A
Authority: CN
Inventors: 弗雷德里克·杜昂
Original assignee: Degremont SA
Current assignee: Suez International SAS
Priority date: 2016-09-27
Filing date: 2017-09-26
Publication date: 2023-12-01
Anticipated expiration: 2037-09-26
Also published as: WO2018060197A1; FR3056600B1; FR3056600A1; US20200032181A1; AU2017333878B2; CN109790501A; EP3519552A1; US12071603B2; AU2017333878A1

Abstract

The invention relates to a device for exposing an algae solution to light for a photobioreactor, the device comprising a flat support (6, 61, 62), the flat support (6, 61, 62) comprising at least one opening (610, 620) capable of supporting at least one tube (5), the tube (5) being made of a liquid-tight, translucent or even transparent flexible material and comprising an open end capable of supporting a sleeve (10), the sleeve being translucent or even transparent and being arranged to seal the tube and to connect the tube to the support, characterized in that the device for exposing light has a positive buoyancy in water. The invention also relates to a photobioreactor provided with such a device and to a method for starting up such a photobioreactor.

Description

Device for exposing an algae solution to light, associated photobioreactor and method of implementation

Technical Field

The present invention relates to the field of production of concentrated algae solutions, and in particular to an apparatus for exposing algae solutions to light. The subject matter of the present invention also relates to a photobioreactor incorporating such a light-exposed device and to a method of starting up such a photobioreactor.

Background

Algae cultures, particularly microalgae cultures, for the production of photosynthetic biofuels or nutraceuticals from algal biomass can only be developed on a large scale by significantly reducing the cost of the photobioreactors and the cost of operating them. Furthermore, algae production is not solely in warm and sunny regions, it is necessary to envisage technical solutions for increasing algae production in countries situated at latitudes of temperate regions.

Photobioreactors are known in the prior art using compartments of different shapes separated by rigid walls, in particular made of polycarbonate or other monomeric or polymeric materials. Thus, document DE10315750 shows a photobioreactor comprising a plurality of rows of rigid transparent vertical tubes in which the flowing algae solution is subjected to light radiation passing through the tubes, which enables photosynthesis to take place. However, for industrial applications where photobioreactors of tens of hectares can be covered, these materials are expensive and the manufacturing time of the components is long. Furthermore, these materials are flammable and their ecological footprint is important for both manufacturing and disposal.

There are also known overground bioreactors which require high financial investments and whose height can lead to wind resistance which is disadvantageous for the construction. Because of their large area contact with outside air, overground bioreactors are very sensitive to climatic conditions, which affect their performance in cold, windy or overheated areas.

From the prior art document WO2013011448A1, a device based on a very thin flexible tube is also known, which assumes a cylindrical shape only because of the static pressure difference between the liquid inside the tube and the liquid in the tank in which the microalgae are cultivated. The flexible nature of the tubes immersed in the culture tank enables them to have a cylindrical shape due only to the difference in height between the internal liquid and the water level of the tank. Thus, without any mechanical stress, the static pressure is evenly distributed over all the height of the tube, which makes it possible to reduce the thickness of the tube while maintaining good mechanical strength. This type of solution makes it possible to envisage the manufacture of compact photobioreactors using extremely light and low-cost materials.

They can be used in existing natural or artificial tanks suitable for continuous cultivation of microalgae. Regular spacing of the sleeves is achieved by mounting perforated plates on a fixed support structure above the pond.

However, the fixation of such support structures is often critical due to the culture area and the liquid charge contained in the tubes.

Furthermore, the installation and fixing of the support structure above the water filled tank is limited by the large number of pipes and accessories required for handling and use of the culture.

This is why one purpose of the invention is to avoid the restrictions imposed by the support structure and in particular to simplify the assembly of the support structure and to fix it to the tank.

Disclosure of Invention

To this end, the invention proposes a device for a photobioreactor for exposing an algae solution to light, which is adapted to be used by making it float in a tank affected by the combination and balance of archimedes 'principle and tropy's principle.

More precisely, the invention proposes a device for exposing an algae solution to light for a photobioreactor, the device comprising a flat support comprising at least one opening capable of receiving at least one tube made of flexible, liquid-impermeable and translucent or even transparent material and comprising an open end capable of receiving a sleeve, the sleeve being translucent or even transparent and adapted to enclose the tube and to fix it to the support, characterized in that the device exposed to light has a positive buoyancy in water, in the sense that the actual weight of the flat support and the non-submerged portion of the tube is less than the archimedes buoyancy caused when it is submerged.

Optional, additional or alternative features of the invention are set out below.

The means for exposing to light may comprise at least one buoyancy buoy or floating structure arranged below the support so as to define a free space between the support and the level of the algae solution.

The flat support may have a positive buoyancy in the water in the sense that the actual weight of the flat support and the non-submerged portion of the tube is less than the archimedes buoyancy that it causes when submerged.

The support may be a frame made of a material having a specific gravity of less than 2, preferably less than 1.

The support may be a porous plate made of a material having a specific gravity of less than 2, preferably less than 1.

The sleeve may comprise an optical concentrator adapted to concentrate light to the interior of the at least one tube.

The cannula may include a valve for allowing liquid into the tube.

The means for exposure to light may also comprise mooring and/or anchoring means.

The subject matter of the present invention is also a photobioreactor for producing an algae solution, comprising a tank and at least one light-exposed means comprising a support comprising at least one opening capable of receiving at least one tube made of flexible, liquid-impermeable and translucent or even transparent material and comprising an open end capable of receiving a sleeve, said sleeve being translucent or even transparent and adapted to enclose said tube and to fix it to the support, characterized in that said at least one light-exposed means is a light-exposed means according to any embodiment of the present invention.

The photobioreactor may include a plurality of light-exposed devices that are assembled together in a manner that increases the light-exposed area of the algae solution.

The photobioreactor may further comprise a pumping means adapted to pump the liquid contained in the at least one tube.

The photobioreactor may further comprise means for replacing the "at least one tube", which replacement means comprise a drum and are adapted to wind and/or unwind the "at least one tube" onto and/or from the drum.

The photobioreactor may comprise means for distributing pressurized gas, in particular carbon dioxide mixed with air or not, in the lower part of the tank, which agitates the algae solution.

The photobioreactor may also include directable reflectors disposed about the perimeter of the photobioreactor to increase the capture area and intensity of light rays, particularly when the azimuth and angle of solar rays are low.

The subject of the invention is also a method for using a photobioreactor according to any one of the embodiments of the invention, characterized in that it comprises in sequence:

a step of assembling at least one device exposed to light,

a step of installing at least one light-exposed device in the empty cell of the photobioreactor,

-a step of filling the tank with a liquid that produces an algae solution.

The method may further comprise the step of filling at least one tube of the at least one light-exposed device with a liquid neutral to the algae solution after filling the cell in order not to degrade the algae solution in case of accidental rupture of the tube.

After the step of filling the at least one tube and when the at least one tube is submerged in the algae solution, the height of the liquid in the tube may be greater than the height of the algae solution to provide a hydrostatic pressure difference for maintaining the shape of the tube without stress.

The method may further comprise the step of mooring and/or anchoring the at least one light-exposed device after filling the at least one pipe.

The method may further comprise, after filling the tank, the step of inoculating the liquid with a microalgae strain to produce an algae solution.

Drawings

Other advantages and specific features of the invention will become apparent from reading the detailed description of non-limiting uses and embodiments, and from the following drawings:

FIG. 1 is a schematic vertical cross-section of a photobioreactor according to the present invention having a tank containing an algae solution.

Fig. 2 is a horizontal sectional view taken along line II-II in fig. 1.

FIG. 3 is a larger scale view of a vertical flexible pipe mounted on a support structure of the vertical flexible pipe.

Fig. 4 and 5 are vertical cross-sectional views of possible shapes of the photo bioreactor tank on a smaller scale.

Fig. 6 is a schematic cross-sectional view of components for securing a flexible pipe to its support structure.

Fig. 7 is a front view of a first embodiment of a structure supporting a flexible tube.

Fig. 8 is a top view of a second embodiment of a structure supporting a flexible tube.

Fig. 9 is a schematic vertical cross-section of a third embodiment of a structure supporting a flexible tube.

For purposes of clarity and conciseness, the reference numbers in the drawings correspond to like elements.

Detailed Description

The embodiments described hereinafter are in no way limiting of the invention, and in particular, variations of the invention may be considered to include only the selection of features described, separate from other features described (even if the selection is isolated in sentences including those other features), so long as the selected features are sufficient to impart technical advantages or distinguish the invention from the prior art. The options include at least one feature, preferably functional and without structural details or with only some structural details, provided these are sufficient alone to confer technical advantages or to distinguish the invention from the prior art.

Referring to fig. 1 of the drawings, a photobioreactor 1, indicated by the abbreviation PBR, for producing a concentrated algae solution 2 can be seen. The PBR comprises a tank 3 containing the algae solution and means for exposing the algae solution to light.

According to the invention, the means of exposure to light comprise at least one support structure or one flat support 6 comprising at least one opening, at least one tube 5 of flexible material, said tube 5 of flexible material being liquid-tight and translucent or even transparent and comprising an open end capable of receiving a sleeve 10, said sleeve being translucent or even transparent and being adapted to enclose said tube and to fix it to the support.

Translucent means that the tube 5 and the sleeve 10 are adapted to allow light to pass through, which light enables photosynthesis reactions in the cell.

Transparent means that the tube 5 and the sleeve 10 are adapted to allow light to pass through (light is transmitted by refraction). In addition, it can be seen clearly through the tube 5 and the sleeve 10.

Still according to the invention, the light-exposed device has a positive buoyancy in water. By "positive buoyancy in water" is meant that the actual weight of the light-exposed device is less than the archimedes buoyancy, which enables the light-exposed device to remain at the surface of the pool and thereby float.

It is advantageous that the entire light-exposed device is associated with a non-submerged portion of the water-filled tube having positive buoyancy.

Buoyancy may be provided in different ways, as described in more detail below.

According to a first embodiment, the means exposed to light may comprise one or more floating buoys 8 connected below the support 6, so that it can float and can remain above the filled pool surface.

According to a second embodiment, the support structure or support 6 has an inherent positive buoyancy and may be a frame 61 made of a material having a specific gravity of less than 2, preferably less than 1. The frame may then comprise a composite of marine particle board or any other low specific gravity corrosion resistant composite material, such as polyurethane, polystyrene doped with glass fibres.

According to a third embodiment, support structure or support 6 has an inherent positive buoyancy and may be a perforated plate 62 also composed of a material having a specific gravity less than 2, preferably less than 1. The material may also be particle board for boats or any other corrosion resistant composite material of low specific gravity, such as polyurethane, polystyrene doped with glass fibers.

Of course, the means of exposure to light may provide a support structure or support 6 composed of a material having a specific gravity of less than 2, preferably less than 1, and additionally one or more floating buoys 8.

In the same detail, the tube 5 is made of transparent flexible material, preferably of traction resistant material. The tube 5 is suspended on a support structure or support 6 and filled with a liquid L giving the tube a cylindrical shape.

The flexible tube 5 is advantageously made of a uv resistant material, in particular of polyurethane terephthalate or similar material. The tube may be produced by rolling up a rectangular portion of the sheet 4 and assembling two parallel edges by gluing or welding or impact. The lower end of the tube is closed while the upper end remains open to secure the tube to the support 6 at its periphery.

As shown in fig. 3, the tubes 5 can be fixed to the support 6 by providing each tube with a truncated cone-shaped opening 7 in the support 6, with a decreasing cross section from top to bottom. The upper edge of the tube 5 is wedged between the frustoconical walls of the opening 7 by means of a sleeve 10, the sleeve 10 itself being frustoconical, associated with the opening 7 and made of transparent material.

The tube 5 may also be secured to the support 6 in a different manner, in particular by a flange or O-ring 106 as shown in fig. 6, rather than being held by a nested conical member. Since there is no contact between the algae solution and the water located in the submerged pipe 5, it is not necessary to provide a complete seal at this fixed level.

Ribs 105 may be provided around the outer surface of the sleeve to prevent the sleeve from passing through the opening of the support when the tube 5 is mounted on the support.

When the support structure is a frame 61, the tubes are inserted between the rods 610 and secured by their bushings, which are also inserted between the rods 610 in a tight fit.

When the support structure is perforated plate 62, tubes are inserted into holes 620 and secured by their bushings, which are also inserted into holes 620 in a tight fit.

The porous plate may be transparent and thin. It may also be reinforced by a transparent reinforcement that provides sufficient surface stiffness to support point loads (cleaning, maintenance).

Grooves capable of collecting rainwater may be provided at both sides of the porous plate. Natural flow ramping may be provided by a pressure differential in the inflatable spacer.

According to the embodiment of fig. 1, the tank 3 is filled with an algae solution 2. A plurality of flexible transparent tubes 5 filled with liquid L are immersed in the algae solution 2 and regularly distributed to transmit and diffuse light captured at the upper ends of the tubes 5 throughout the tank and the algae solution 2.

According to this embodiment, the main function of the liquid L of the filling tube 5 is to transmit and diffuse the captured light, and the liquid L is composed of water and additives in particular (the additives may be antifreeze products, fluorescent products or antiseptic products or anti-foaming products). The closed lower end of the tube 5 is preferably provided with ballast 11. The ballast 11 makes it possible to prevent the empty pipe from floating when added to the algae solution 2, so as not to be difficult to fill with water later. The ballast may take the form of a rod or heavy sphere of metal or mineral material.

The composition of the liquid L of the filling tube 5 is neutral with respect to the algae solution, so as to avoid all risks in case of accidental rupture. In the embodiment of fig. 1, the liquid L is essentially water, possibly containing additives, and the additives may be antifreeze products, corrosion protection products or fluorescent products.

The height h5 of the liquid in the tube 5 is slightly greater than the height h2 of the algae solution in the tank (fig. 1) to create a hydrostatic pressure difference (h 5-h 2) that maintains the cylindrical shape and does not create stress on the flexible walls of the tube 5. The height of the sleeve support at the algae solution level is a result of the balance between archimedes buoyancy and the weight carried by the porous plate and the non-submerged portion of the tube.

Advantageously, the tube is filled with water reaching the sleeve 10. This allows the propagation velocity of light in the tube to occur substantially in water without discontinuous transmission. The transmission then has the same quality as the optical fiber transmission.

Also, leaving no air in the tube makes it possible to prevent mist from forming on the inner surface of the wall, thereby preventing a possible formation of a barrier to light.

The outer wall of the tube 5 is in contact with the algae solution 2 filling the pond.

To optimize the "light wall" properties of the tube, it is advantageous to add an optical concentrator 104 to the sleeve to concentrate the light into the interior of the tube. Thereby increasing the brightness of the inside of the tube 5. To this end, and as shown in FIG. 6, the sleeve 10 may include a body 101 that houses a Fresnel lens. The sleeve may be sealed in a sealed manner by a translucent or even transparent cover 102, the cover 102 may also include an optical concentrator.

Advantageously, the sleeve may comprise a valve 103 for letting liquid into the tube when filling the tube with neutral liquid. The valve is then preferably located on the cap 102 of the tube.

As shown in fig. 9, the pool 3 may comprise a plurality of light-exposed devices according to the invention interconnected by buoys 8.

A supplemental inflatable buoy may then be provided regularly and laterally spaced from the main structure. They can then support high point loads (snow or maintenance tools) without causing residual deformation of the surface. Advantageously, the means exposed to light may also comprise mooring and/or anchoring means (not shown in the figures). In fact, due to the positive buoyancy of the device, it is not necessary to fix the device to the surface of the PBR tank as in the prior art. If it is desired to position the light-exposed devices in the exact location of the pool, or if there are multiple light-exposed devices that may collide, it is therefore necessary to moor them at fixed points outside the pool or anchor them at the bottom of the pool.

As shown in fig. 2, the cells may be square or rectangular, or may be cylindrical (not shown) with a circular cross-section. As shown in fig. 1, the tank may be above ground, in which case portholes 12 may be provided in the wall to effect exposure of the algae solution 2 to light. The pool 3 may also be partially or completely underground. The pool can also be made of prefabricated elements in the factory and assembled in situ with sealing covers (liners) of the type used in swimming pools.

As shown in fig. 4, the vertical section 13 of the cell may be rectangular and have a flat top. As shown in fig. 5, the vertical section 14 may alternatively have a lower portion with a trapezoidal shape.

In the case of above-ground or partially below-ground tanks, the wall may also be made of a transparent liquid-impermeable film, in particular a flexible film, so that the algae solution is exposed to light.

A pipe 25 for extracting the algae solution is provided in the upper part of the tank in order to benefit from the higher concentration of algae. After extraction and filtration, the water is returned to the lower part via conduit 26. Nutrients for algae development can be injected into the returned water.

The process of extracting biomass in the algae solution from the photobioreactor is continuous and because it thus does not require intermediate storage in the tank, ultrafiltration with membranes is not necessary to prevent unwanted development of algae in the tank.

To optimize the photosynthesis reaction, the photobioreactor according to the present invention may provide a system for filtering the wavelength of light.

Still for this purpose, the photobioreactor may also be provided with a visor to reduce the light intensity of the light rays incident on the cell surface. The material of the outer lens may be colored or photochromic to limit the intensity of the captured light.

Likewise, the photobioreactor may also be provided with artificial lighting means, such as light emitting diodes.

The photobioreactor may further comprise directable reflectors arranged at the periphery of the photobioreactor in a manner that increases the capture area of the incident radiation and in a manner that increases the light intensity when the azimuth angle and angle of the solar rays are low.

The photobioreactor according to the invention may provide means for evacuating the tube to replace it and installing another tube.

The cell can be emptied without dismantling the pipe, in which case the pipe will form a number of "columns" by significantly increasing the static pressure inside it and below the pipe.

The tube to be removed is connected at its upper end to a pipe inserted into the inlet of the device for sucking the liquid in the tube. The suction device is usually constituted by a pump. The external pressure exerted by the algae solution compresses the cannula, flattening the cannula, and removing the cannula from the well after disconnecting the suction conduit.

Above the tank a winding device for the replacement tube is arranged. The apparatus includes a rotating winding drum mounted for translational movement over the cells of the pool (e.g., on a moving gantry) while supported by rails or slots. Cleaning members, particularly rotating brushes, are provided to translate with the rollers and define vertical channel gaps for the flat tubes, which are cleaned with these brushes when removed from the algae solution. The device is capable of unwinding a flat fresh tube, placing it in the algae solution to replace those that have been removed.

In the lower part of the tank, the PBR comprises means for distributing compressed gas, in particular carbon dioxide (CO 2) mixed with or not with air, in order to promote the development of the algae and to agitate the algae solution. The distribution means consist of a manifold which is able to blow gas into the space between the tubes 5, as indicated by the arrow F. The distribution device 27 is connected to the outlet of a rotary piston compressor or screw compressor 28 by a pipe 29. The distribution of carbon dioxide (CO 2) agitates and homogenizes the algae solution in the tank 9.

The fact that the device carrying the pipe floats at a distance from the surface of the tank (e.g. due to a buoy lifting the device) enables the gas to escape easily.

Some of the gas escaping from the upper part of the tank can be captured and recovered for better carbon dioxide (CO 2) removal. For this purpose the PBR further comprises a gas capturing device 30, which gas capturing device 30 is formed by a pipe opening in the upper part of the tank 9, which pipe opening is above the algae solution and in the gaseous atmosphere above the solution. These capturing devices are connected to the suction side of an exhaust fan 31, which exhaust fan 31 discharges the gas into a duct 32, in particular to the atmosphere. Some of this gas may be recycled due to the discharge 33 on the conduit 32 connected to the suction side of the compressor 28.

The tank 3 is insulated to reduce heat losses. Advantageously, the temperature of the algae solution is regulated by means (not shown) for heating and/or cooling the water introduced into the tank through the conduit 26 after filtration, so that optimal conditions for algae and microalgae growth can be maintained.

As the known heating means, there can be mentioned a heating floor to which low and medium temperature hot water is supplied, which is bubbled with saturated sludge or combustion gas filled with CO 2; plate, tube or spiral external combustion heat exchangers; an immersed or self-regulating external electrical heating element.

Supplemental insulation devices may be used with double walls for the tube support.

The method of starting up a photobioreactor according to the invention now first requires the assembly of at least one light-exposed device. The assembly is preferably performed in a dry dock in the pool, but may also be performed outside the pool. After assembly, i.e. after insertion of the tube into its support through its sleeve, one or more light-exposed devices have to be positioned at the bottom of the empty cell of the photobioreactor. The pool is then filled thoroughly with the liquid that produces the algae solution. In other words, when the whole device is assembled, the actuation means enable the structure of the PBR to gradually rise when the tank is full of water, until its operating level is reached.

After filling the cell, the tube may be directly filled with a liquid neutral to the algae solution so as not to degrade the algae solution in case of accidental rupture of the tube.

Advantageously, when the tube is immersed in the algae solution, the height of the liquid in the tube (h 5) is greater than the height of the algae solution (h 2) to ensure a hydrostatic pressure difference for maintaining the shape of the tube without stress.

The cylindrical and vertical shape of the flexible tube is thus maintained by the differential static pressure between the liquid in the tube and the liquid in the tank, which is slightly below the level of the liquid in the tube (this is related to the Torr principle). This pressure differential is constant over all the height of the pipe, regardless of the height at which the pipe is submerged. This significantly limits the internal pressure stresses on the flexible material of the tube.

In practice, the submerged height of the pipe is related to the archimedes buoyancy exerted on the floating structure of the pipe support. This upward force causes a height difference between the liquid in the tube and the top water level of the tank. In summary, it is a balance between the archimedes principle and the toberculosis principle, so that the tube can be maintained.

To stabilize all light-exposed devices, the light-exposed devices may be moored and/or anchored together or at the perimeter of the pool.

Finally, a step of inoculating the liquid with a microalgae strain to produce an algae solution may be performed.

It should be noted that the benefits of buoyancy of the light-exposed device are very particularly exhibited when using a photobioreactor according to any of the embodiments described above.

In fact, with the prior art devices, it is necessary to firmly fix the support on the ground surrounding the tank, and then to mount these elements on the tank one after the other. The assembly, installation and operation of the elements above the pool is then uncertain and requires appropriate transport and lifting machinery (for example, on a barge). In addition, personnel safety severely impacts time and infrastructure. If some devices fall into the pool, the operation will be delayed accordingly.

Thus, the floating nature of the light-exposed device allows for simplified use of the light-exposed device and allows it to be fixed at a lower cost.

It should also be noted that the buoyancy of the light-exposed device makes the design very modular. In fact, since it is not necessary to fix them at the perimeter of the cell, additions, removals or modifications can be made while the cell is running.

In other words, these light-exposed devices are highly autonomous in terms of use (installation, lifetime).

Moreover, the position of the tube of the device exposed to light relative to the water surface is always the same, regardless of the water level in the tank.

A supporting structure for placing the foot rest on the ground is not required.

Whether filled or not, the light-exposed device can be assembled at a location remote from the cell and translated over the cell.

There is only a small risk of damage associated with a change in the water level in the sump.

The assembly is rapid and no heavy lifting device is required.

The overall dimensions of the device when disassembled meet road transport loading specifications, i.e. the maximum overall dimensions are 2.5m.

Recycled materials may be used as structures and buoys.

Of course, the invention is not limited to the embodiments just described and many modifications may be made to those embodiments without departing from the scope of the invention. Furthermore, the various features, shapes, variations and embodiments of the invention may be associated with each other in different combinations, provided that they are not mutually exclusive or incompatible.

Claims

1. A device for exposing an algae solution to light for a photobioreactor, the device comprising:

a flat support (6) comprising at least one opening able to receive at least one tube (5),

a tube (5) made of a flexible, liquid-tight and translucent or even transparent material and comprising an open end capable of receiving a cannula (10),

a sleeve, which is translucent, or even transparent, and is adapted to enclose the tube and to fix the tube to the support,

characterized in that the light-exposed means has a positive buoyancy in water in the sense that the actual weight of the light-exposed means is less than the Archimedes buoyancy caused by its immersion,

the means of exposure to light comprise at least one buoyancy buoy (8) for a flat support (6), the buoyancy buoy (8) being arranged below the support so as to define a free space between the support and the algae solution level, such that gas easily escapes,

the light-exposed device floats on the surface of the tank filled with the algae solution, and

the tube (5) is filled with a liquid that is neutral with respect to the algae solution, and the height (h 5) of the liquid in the tube (5) is greater than the height (h 2) of the algae solution to provide a hydrostatic pressure differential for maintaining the shape of the tube without stress.

2. The light-exposed device according to claim 1, characterized in that the flat support (6) has a positive buoyancy in water in the sense that the actual weight of the flat support is less than the archimedes buoyancy caused by its immersion.

3. The light-exposure device according to any one of claims 1 to 2, characterized in that the support is a frame (61) composed of a material having a specific gravity of less than 2.

4. The light-exposure device according to any one of claims 1 to 2, characterized in that the support is a frame (61) composed of a material having a specific gravity of less than 1.

5. A device exposed to light according to any one of claims 1 to 2, characterized in that the support is a perforated plate (62) composed of a material having a specific gravity less than 2.

6. A device exposed to light according to any one of claims 1 to 2, characterized in that the support is a perforated plate (62) composed of a material having a specific gravity less than 1.

7. The light-exposure device according to any one of claims 1 to 2, characterized in that at least one sleeve comprises an optical concentrator (104) adapted to concentrate light to the interior of at least one tube.

8. A device according to any of claims 1-2, characterized in that at least one sleeve comprises a valve (103) for letting liquid into the tube.

9. Light-exposed device according to any one of claims 1 to 2, characterized in that it further comprises mooring and/or anchoring means.

10. A photobioreactor for producing an algae solution, comprising a tank (3) and at least one light-exposed device, the light-exposed device comprising:

characterized in that the at least one light-exposed device is a light-exposed device according to any one of claims 1 to 9.

11. The photobioreactor according to claim 10, characterized in that it comprises a plurality of light-exposed means assembled together in such a way as to increase the light-exposed area of the algae solution.

12. The photobioreactor according to any one of claims 10 to 11, characterized in that it further comprises suction means adapted to suck the liquid contained in the at least one tube.

13. The photobioreactor according to any one of claims 10 to 11, characterized in that it further comprises means for replacing at least one tube, which replacement means comprise a drum and are adapted to wind and/or unwind at least one tube onto/from the drum.

14. A photobioreactor according to any one of claims 10 to 11, characterised in that it comprises means for distributing pressurized gas in the lower part of the tank (3), said means agitating the algae solution.

15. Photobioreactor according to any one of claims 10 to 11, characterized in that it comprises means for distributing carbon dioxide (CO 2) mixed with air or not mixed with air in the lower part of the tank (3), said means stirring the algae solution.

16. The photobioreactor according to any one of claims 10 to 11, characterized in that it further comprises a directable reflector arranged at the periphery of the photobioreactor in order to increase the capturing area and intensity of the light rays.

17. A method of using a photobioreactor according to any one of claims 10 to 16, characterized in that it comprises in sequence:

a step of assembling at least one device exposed to light according to any one of claims 1 to 9,

-a step of filling the tank with a liquid that produces an algae solution.

18. The method of using a photobioreactor as recited in claim 17, further comprising the step of filling at least one tube of the at least one light-exposed device with a liquid neutral to the algae solution after filling the cell in order not to degrade the algae solution in the event of accidental breakage of the tube.

19. The method of using a photobioreactor as recited in claim 18, wherein the height (h 5) of the liquid in the tube is greater than the height (h 2) of the algae solution when at least one tube is submerged in the algae solution to provide a hydrostatic pressure differential for maintaining the shape of the tube without stress.

20. A method of using a photobioreactor as claimed in claim 18 or 19, further comprising the step of mooring and/or anchoring at least one light-exposed device after filling the at least one tube.

21. The method of using a photobioreactor as recited in any one of claims 18 to 19, further comprising the step of inoculating the liquid with microalgae strains to produce an algae solution after filling the tank.